The present invention relates to a process for the recovery of zinc, lead, silver and gold from impure jarosite precipitates which contain the said metals and are derived from zinc processes, in connection with an electrolytic zinc process, especially the process disclosed in Finnish Patent Application No. 803096.
Finnish Patent Application No. 803096 discloses a process by which, in connection with an electrolytic zinc process--especially the leach process for zinc calcine in accordance with Finnish Patent Application No. 410/73--the recovery of lead, silver and gold is carried out in an economical and simple manner in addition to a high recovery of zinc, copper and cadmium.
The specification of Finnish Patent Application No. 803096 describes the current state of the art in the field of leaching processes for zinc calcine. In this context, it has also become evident that in the waste disposal areas of several zinc plants there have accumulated considerable amounts of jarosite precipitates derived from leaching processes for zinc calcine, and that these residues usually always contain some amount of zinc ferrite which has not reacted during the process, uncalcined zinc concentrate, and some or all of the lead, silver and gold contained in the concentrate feed of the plant.
The changes in the relative prices of metals in recent years--especially the sharp increase in the prices of noble metals--have lead to the current situation in which not only the zinc, copper and cadmium but also the lead, silver and gold present in the concentrates must be recovered in a competitive zinc process. This has also lead to a crucially altered situation with regard to the jarosite precipitates which were previously directed to waste disposal areas. Previously the precipitates concerned were regarded as having no or little value. Now, however, they have gained economic value owing to the zinc, lead, silver and gold contained in them; this value has been affected, on the one hand, by the changed relative prices of the metals and, on the other hand, by new alternative processes for which the jarosite precipitates of the type discussed can be considered sources of raw material from which the said metals can be recovered economically.
The object of the present invention is to provide a process by which the zinc, lead, silver and gold present in jarosite precipitate are recovered economically--in connection with the leaching process for zinc calcine disclosed in Finnish Patent Application No. 803096--from precipitates in waste disposal areas, which have been derived from a zinc process and contain zinc, lead, silver and gold.